There is currently much interest in and great need for techniques for removing halogenated organic compounds such as polychlorinated biphenyls (PCB's), dioxins, methylene chloride, PAHs, and trichloroethylene from various contaminated environments, particularly soil and water. Flushing and soil washing techniques may be effective in some respects for removing some of these compounds, but the hydrophobic nature of compounds such as the PCB's impedes water-based flushing. Moreover, the volume of contaminated wash liquid presents further handling and clean up problems.
Very significant improvement in the removal of the organic compounds has been realized by the use of aqueous solutions which contain surfactants which increases the water-solubility of the compounds. Surfactant-assisted flushing techniques can result in removal efficiencies of more than about 90%.
However, there are several important considerations associated with the use of surfactant-assisted flushing. For example, the surfactant itself must be environmentally safe, as well as being easily removable from the medium being treated, e.g., contaminated soil. Furthermore, some surfactants may disperse soil or clay particles in such an environment, resulting in the clogging of soil pore spaces. This could lead to diversion of the surfactant from the contaminated area, and a decrease in the efficiency of the entire process.
Moreover, in using aqueous surfactant solutions as a wash liquid, the surfactant and the contaminant (e.g. PCB's) can usually be readily removed from the water, but it is often difficult to selectively remove only the contaminant from the wash liquid thereby leaving a reusable surfactant-containing wash liquid. It has generally not been possible to efficiently recover the surfactant solution for reuse.
One technique for treating aqueous surfactant-contaminant solutions resulting from surfactant flushing involved hydrolysis of the surfactant, as described in Treatment of Contaminated Soils with Aqueous Surfactants, W. E. Ellis et al., U.S. EPA Report No. EPA/600/2-85/129, PB 86-122561, 1985. However, such a technique breaks down the surfactant, thereby making recycling impossible.
Another attempt at removing both a PCB contaminant and a surfactant from an aqueous solution involved the use of a PCB-anionic surfactant coprecipitation technique, as described by J. B. McDermott et al. in Environ. Prog., 1989, 8(1), pp 46-51. However, that technique also does not allow the surfactant to be recycled.
Other methods which have also been considered for removing both the organic contaminant and the surfactant from the contaminated medium include leaching accompanied by foam fractionation or adsorption techniques (e.g., the use of clays or activated carbon). However, the relatively high content of surfactants present in the leachate may not make these processes practical.
It is therefore apparent that a need exists for an improved process for removing various hydrophobic organic contaminants from a solid or liquid environment. The process should permit sufficient concentration of contaminants at an efficient absorbing rate. Furthermore, the process should also allow for the recycling of any assisting components, such as aqueous surfactants and should not liberate any constituents which would cause ancillary contamination of the environment being cleaned. The term "sorb" and any derivative thereof as used herein is intended to include adsorption and absorption as the case may be.